Make sure audio is on from TOSLINK cable and try to record. I was successfull to record stereo stream (PCM 2.0) coming from my Samsung Smart TV:

I didn’t try to send Dolby 5.1 or DTS sound through TOSLINK, but I believe Sandberg USB Sound Box 7.1 supports stereo only through digital ports. When I bought the device I had hard time trying to output Dolby 5.1 through S/PDIF to home theatre system – all it was receiving was PCM 2.0, so I assume input is stereo-only as well.